DESCRIPTION: There is persuasive epidemiological evidence that consumption of dietary carotenoids, particularly beta-carotene, reduces cancer risk at many sites. Laboratory studies also support a protective role for beta-carotene and many other dietary carotenoids. Yet clinical intervention trials with purified beta-carotene have failed to show protection. This proposal seeks to resolve this paradox and achieve a more complete understanding of the pharmacology and molecular biological actions of two major dietary carotenoids, lutein and lycopene. Dr. Bertram and colleagues have identified two carotenoid derivative formed after ingestion of the parent compounds that possess biological activity. This application will compare and contrast the activity of these derivatives with that of the parent compound for their ability to 1) inhibit neoplastic transformation in a model animal cell system, 2) alter the differentiation state of human keratinocytes in organotypic culture, 3) alter the expression of connexin43, a potential intermediate marker of response, in mouse and in human keratinocytes. It is also proposed to examine the molecular mechanism whereby these carotenoid derivatives are anti-proliferative by use of flow cytometry and antibodies to cell cycle regulatory proteins. Finally, the project will examine the molecular mode of action of these derivatives by examining 1) their ability to activate nuclear receptors by monitoring transcriptional activation of genes controlled by known responsive elements after transfection with reporter constructs containing these responsive elements together with the appropriate nuclear receptor, 2) by use of ligand-specific antagonists. Should these studies indicate that derivatives of dietary carotenoids, rather than the parent carotenoids, are responsible for many of the biological effects attributed to these compounds, new approaches to cancer prevention would be indicated and a route opened to develop new classes of biologically active compounds.